The other day, I received an e-mail on Classmates.com from a former high school classmate. This reminded me of how, when I had first arrived in the U.S. in the 9th grade, a number of rotten psychopaths would "borrow" pencils from me and neglect to return them. Therefore, I instituted a practice that students who wanted to borrow pens or pencils would have to pay a deposit. When I first instituted this policy, one student asked if he would get the deposit back when he returned the pencil. With my most cynical and doubtful voice, I said "If you're lucky." The student got somehow worried, but we agreed that he actually get the deposit back, not just if he "[were] lucky." On another occasion, both I and another student who had given his paycheck in deposit forgot about the loan, so I ended up keeping his paycheck over the week-end. $68 and change were a lot of money back then.
Just in case you are wondering, Audy--who reminded me about this practice--so far as I remember always returned my pens. One time, I was a bit disappointed since he had put up a $50 bill in deposit.